Great finding! No worries it'll be removed in the next update. At the moment you can remove the line manually.

File: /wpforo/classes/UserGroups.php

Remove the following lines:

file_put_contents(ABSPATH . '/logggging-R.txt', print_r($ugids, true) . "\r\n", FILE_APPEND);
file_put_contents(ABSPATH . '/logggging-UR.txt', print_r($usergroupid_role, true) . "\r\n", FILE_APPEND);
file_put_contents(ABSPATH . '/logggging-RL.txt', print_r($role, true) . "\r\n", FILE_APPEND);

I almost had a heart attack. You create files in the root of the site and it took me hours to find the cause. 3 files.

Usergroups.php - 21.117 bytes - 14.09.23 at 19:38 - \Wp-content\Plugins\Wpforo\Classes\
17.580 file_put_contents(ABSPATH . '/logggging-UR.txt', print_r($usergroupid_role, true) . "\r\n", FILE_APPEND);

For god's sake guys ...